The invention relates to an apparatus and method for forming a wear-resistant metal composition. In particular, the invention relates to forming of a wear-resistant magnesium or magnesium alloy.
It is common practice to mix solid additives, such as metal oxides, with magnesium or other materials to improve the wear resistance of the metal. For example, aluminum oxide, magnesium oxide, or mixtures thereof, are blended with a partially liquid magnesium or magnesium alloy matrix to give a magnesium composite in which the solidified product has good wear resistance. Improving the wear resistance of the magnesium product makes it useful for fabricating various articles, such as rollers, pulleys, cylinder liners, pistons, and other devices. Since the solid oxide materials are highly insoluble in the partially liquid metal matrix, it is difficult to achieve good distribution of the solid additives in the base metal. Recent methods have been developed in which up to about 30 weight percent of an insoluble material can be blended with a metal matrix which is at least partially liquid, that is, the metal is in a thixotropic state. Some of these methods are described in U.S. Pat. Nos. 3,948,650; 3,951,651; and 4,174,214. Such methods have several drawbacks in that they require careful temperature control, special equipment for melting, and agitation of the base metal.
The present invention overcomes some of the problems described above by providing an apparatus and method for forming a wear-resistant metal in which the insoluble solid additives are added to the base metal while the base metal is in a molten state.